Ill . Periodicity of the Sexual Cells in Dictyota. 557 
oogonia and antheridia. Some of the oogonia were small, being equivalent 
to half- or quarter-antheridia. When liberated none of the oospheres 
attracted the antherozoids, but some of them divided parthenogenetically 
and then died. 
17. Haliseris seems to have a similar periodicity in the development of 
the sexual cells, but the details of the process have not as yet been fully 
worked out. As surmised by Johnson, the antherozoids are ciliate. They 
are also very active, and the unfertilized eggs show the same partheno- 
genetic phenomena as do the eggs of Dictyota. 
Having discovered a plant whose sexual reproduction shows such 
remarkable response to external stimuli, it is evidently desirable that obser- 
vations such as have been here attempted should be made on other coasts, 
and at the same time be made much more detailed and accurate. My 
apology for the incompleteness of my own is that they were really only 
incidental to my cytological work on the group, and made under great diffi- 
culties in the short intervals obtained during professional work. If such 
work be taken up by other algologists, I hope this paper will be of some 
assistance in setting about the initial steps. To perform such a task 
successfully, it would be necessary to, find a habitat such as the Swillies, 
where an abundance of clean and healthy plants could be obtained. Plants 
should be collected and examined at least every alternate day, records 
should be made from healthy mature plants only, and full particulars should 
be kept of the times and heights of the tides, and — a point which I omitted 
to mention in the body of the paper — the direction and force of the wind and 
the state of the barometer should be entered, for the two things frequently 
modify very materially the tides as given in the tidal almanac. In fact, 
the only method of dealing satisfactorily with the tides would be to have 
a self-recording tide-gauge : this would give an absolutely faithful record 
of the height of the water at any given moment. In addition to this it 
would be necessary to accurately measure the amount of light obtainable 
at different periods of the tide and the variations of temperature. Were 
this sort of accurate work done at a number of stations, it would form 
a valuable contribution to our knowledge of the response given to external 
stimuli by the reproductive process in this plant. 
I gratefully beg to express my obligation to the Council of the Royal 
Society for giving me a grant of money to enable me to carry on my study 
of the Dictyotaceae on the South Coast, and also to the Royal Microscopical 
Society for nominating me to their table in the Marine Biological Labora- 
tory at Plymouth. To Dr. Allen, the Director of the latter institution, and 
his assistant, Mr. Smith, I also wish to express my deep obligation for their 
unfailing courtesy and their readiness to place the resources of the establish- 
ment at my disposal. It is a matter of surprise that so few algologists take 
advantage of such a well-equipped and admirably conducted station. 
